1. Field of the Invention
The present invention relates to radiation therapy. More specifically, the present invention relates to a system, apparatus, software, and related methods for analyzing a geometry of a patient treatment apparatus.
2. Description of the Related Art
Radiation therapy can be effective in treating certain types of cancerous tumors, lesions, or other “targets.” A vast majority of such targets can be eradicated completely if a sufficient radiation dose is delivered to the tumor or lesion volume. Complications, however, may result from use of the necessary effective radiation dose, due to damage to healthy tissue which surrounds the target, or to other healthy body organs located close to the target. The goal of various radiation procedures such as conformal radiation therapy treatment is to confine the delivered radiation dose to only the target volume defined by the outer surfaces of the target, while minimizing the dose of radiation to surrounding healthy tissue or adjacent healthy organs. If the effective radiation dose is not delivered to the proper location within the patient, serious complications may result.
Radiation therapy treatment typically uses a radiation delivery apparatus, such as, for example, a linear accelerator or other radiation producing source, to treat the target. The conventional linear accelerator includes a rotating gantry which generally rotates about a horizontal axis and which has a radiation beam source positionable about the patient which can direct a radiation beam toward the target to be treated. The linear accelerator can also include a rotating treatment table which generally rotates about a vertical axis and which can position the target within a rotational plane of the rotating gantry. Various types of devices or apparatus can further conform the shape of the radiation treatment beam during rotation of the radiation beam source to follow the spatial contour of the target, as viewed with respect to the radiation treatment beam, as it passes through the patient's body into the target. Multileaf collimators, for example, having multiple leaf or finger projections can be programmed to move individually in to and out of the path of the radiation beam to shape the radiation beam.
Various types of radiation treatment planning systems can create a radiation treatment plan which, when implemented, will deliver a specified dose of radiation shaped to conform to the target volume, while limiting the radiation dose delivered to sensitive surrounding healthy tissue or adjacent healthy organs or structures. Typically, the patient has the radiation therapy treatment plan prepared based upon a diagnostic study utilizing computerized tomographic (“CT”) scanning, magnetic resonance (“MR”) imaging, or conventional simulation films which are plain x-rays generated with the patient. This radiation therapy treatment plan is developed such that the patient's tumor or lesion is in the position that will be used during the radiation therapy treatment.
Regardless of which technique is used at the time of the diagnostic study to develop the radiation therapy treatment plan, in the delivery of either conformal radiation therapy treatments or static radiation therapy treatments, the position of the target with respect to the radiation delivery device or apparatus is very important. Successful radiation therapy depends on accurately placing the radiation beam in the proper position upon the target. Thus, it is necessary to relate the position of the target at the time of the diagnostic study to how the target will be positioned at the time of the radiation therapy treatment. It is also necessary to maintain an alignment between the radiation delivery device or apparatus and the target throughout the delivery of the radiation therapy. If this positional relationship is not correct, the radiation dose may not be delivered to the correct location within the patient's body, possibly under-treating the target tumor or lesion, and damaging healthy surrounding tissue and organs.
Thus, proper radiation therapy depends on accurately placing radiation beams in a proper juxtaposition with the patient to be treated. This can be accomplished by referencing both the radiation beam and the patient position to a coordinate system referred to as the isocenter coordinate system, which is defined by the geometry of the radiation delivery device or apparatus. In the linear accelerator example, the gantry, the treatment table, and collimator each have axes of rotation designed to intersect at a specific position in the middle of a treatment room, referred to as the isocenter, the origin of the isocenter coordinate system. The isocenter coordinate system is typically nominally defined as horizontal x-axis), vertical (z-axis), and co-linear with the axis of gantry rotation (y-axis). The intersection (isocenter) of these three axis of interest is determined and used as a reference “point” to orient the target to the radiation treatment plan and for execution subsequent radiation delivery.
In order to deliver the radiation therapy in accordance with the radiation plan, the position of the patient is generally adjusted to dispose the target at the isocenter of the linear accelerator. That is, the patient is positioned on the treatment table of the radiation delivery device or apparatus to conform to the position used during formulation of the treatment plan. The treatment table is rotated to dispose the target at the isocenter to align the view of the target with that view expected by the collimator or other radiation delivery device of the linear accelerator, according to the radiation treatment plan. The treatment table is then locked in place, and the patient is immobilized so that the radiation therapy treatment can be started.
In the linear accelerator example, the isocenter can be considered to be the point where the radiation beams from the collimator intersect as the gantry of the linear accelerator carrying the radiation beam source rotates around the target in the patient. There are various methodologies of determining the location of this isocenter. For example, one methodology of determining the isocenter includes attaching a marking device to the gantry, such as a long rod holding a marking implement, and positioning a vertically oriented sheet of receiving material, such as paper, adjacent the marking device. The gantry is then rotated to form an arc or a circle on the receiving material. The operator can then examine the arc or circle to determine the origin of the arc or circle, which relates to the isocenter. Also, for example, the operator can actually deploy the radiation beam in order to measure the direction of the radiation beam during rotation of the gantry, to thereby determine the location of the isocenter. Other physical measurements can also be taken to help the operator determine an approximate location of the isocenter. Lasers, typically mounted on the wall of the treatment room, are pointed or directed to cross at this isocenter to identify the predetermined location of the isocenter. Phantoms (patient structure simulators) positioned on the treatment table are typically utilized to perform such laser alignment.
Recognized by the Applicant, however, is that current methods of determining the isocenter are difficult and time-consuming and have inherent inaccuracies because they, at least in the linear accelerator example, fail to properly account for the collimator and/or the treatment table. Also, the mechanical systems including the gantry, collimator, and treatment table are known to be imperfect, and thus, do not produce absolutely true circular arcs of rotation. For example, the bearings of the linear accelerator are not true spheres and the gantry itself may tend to sag. Thus, the arc or circle formed to determine the location of the isocenter are imperfect, and therefore, do not produce perfect centers of rotation nor perfect axes of rotation. This results in a non-precise isocenter position. The state-of-the-art tends to ignore or misinterpret these imperfections, and therefore, produces an inherently inaccurate isocenter position.
Also, as described above, recognized is that lasers are known to drift and in other ways degrade in performance. Thus, the lasers can result in further inaccuracies being inherently added to the isocenter position which need be precise to properly define the coordinate system used by the operator to deliver the correct radiation treatment. Recognized, therefore, is the need for a system, software, and methods that can precisely measure the rotation of various components of the mechanical system of the radiation treatment device or apparatus to determine the location of the radiation beam (e.g. from the geometry of the gantry and collimator) and the positioning of the patient (e.g. from the geometry of the treatment table) in order to precisely define the coordinate system used by the operator to deliver the correct treatment.